Green tea, or Camellia sinensis, is estimated to be the second most consumed beverage in the world, with water being the first. Epidemiological studies indicate that green tea consumption is associated with several health-promoting benefits, including the support of healthy body weight and cardiovascular health. Recent research is investigating the beneficial role of green tea on the immune system.

The main polyphenolic compounds in green tea are catechin flavonoids. Roughly 50% to 80% of catechins in a 200 mg to 300 mg brewed cup of green tea consists of a subtype called epigallocatechin-3-gallate (EGCg). EGCg is the most well-studied compound in green tea, which is considered to be the active ingredient. Although EGCg can be obtained through green tea consumption, it is also generally well tolerated as a supplement at low quantities based on a systematic review.

A recently published review article by Wang and colleagues examined the immunomodulatory effects of green tea polyphenols. Although the exact immunomodulatory pathways of green tea are not fully understood, the researchers describe several mechanisms through which EGCg may support the immune system. For instance, animal studies demonstrate EGCg may stimulate humoral immunity through B-cell proliferation and antibody production, enhance cellular immunity through T-cell lymphocyte activation and transformation, modulate pro-inflammatory factors, and decrease oxidative stress by neutralizing reactive oxygen species (ROS).

EGCg may also support a healthy gastrointestinal microbial environment, thereby supporting overall immune health. In vitro studies suggest that EGCg may mitigate bacterial biofilms that play a role in some infections. Animal models further suggest EGCg may benefit those with obesity-related immune dysfunction. Adipose tissue has been shown to release pro-inflammatory cytokines and induce ROS production. Animal models indicate EGCg may support those with T-cell-mediated autoimmune diseases. However, more human research study is needed. 

Catechin flavonoids may be helpful in promoting upper respiratory tract health and healthy microbial environments, such as in the case of a common cold. However, there is a need for further studies to confirm their clinical efficacy.

A randomized, double-blind, placebo-controlled study (n = 109) administered either a placebo or 490 mg of catechins (59% EGCg) to healthy individuals to observe the effect of catechins on the duration and severity of upper respiratory tract infections (URTIs) in winter. Compared to the placebo, the subjects who received the catechin administration displayed a significantly reduced duration of a runny nose, nasal congestion, headaches, and overall URTI duration. 

The antioxidative and anti-inflammatory properties of EGCg are well known. EGCg may support the immune system, healthy microbial environments, gut health, and upper respiratory tract health. 

By Danielle Moyer, MS, CNS, LDN